There was a short discussion a few months ago about Section 6.1 of an expired SFTP drafts. I used Version 3 as the baseline as that is the version which OpenSSH implemented. In my opinion it would be easier to document Version 3 as an IETF specification instead of trying to pursue the previous efforts.
Van Dyke software seems to have implemented features from the later SFTP drafts in their products. I have used them, and can say that they are useful in getting a more faithful transfer of files between Windows systems.